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This invention relates to the splicing together of webs made of two plastic materials. More particularly, the present invention relates to an improved method and a web splice assembly or machine for repeatedly heat-seal splicing the trailing end of a first, two-sided plastic material web and the leading end of a second, two-sided plastic material web together; then when the second web is running, for heat-seal splicing the trailing end of the second web and the leading end of a third, two-sided plastic material web together; and so forth.
Web splicers have been used in the past in the manufacture of disposable diapers, which are made, in part, by combining webs of various materials, one on top of another, in a relatively high speed, continuous manufacturing process. The combined webs include polyethylene, and various absorbent and hydrophilic inner liners that have different modula of elasticity and that readily inelastically deform under even low tensions. Additionally, two-sided plastic material webs may be used. In this regard, one surface of a low density polyethylene web may be xe2x80x9crougherxe2x80x9d than the other surface because of micro-embossing. When such two-sided webs are to be spliced, it is important that after splicing, like or similar surfaces face in the same direction when the webs run through a subsequent process.
Splices are usually accomplished by tape splicing machines that applied tape to abutted leading and trailing ends of the webs to be spliced. As a practical matter, there is no reliable way of quickly determining, downstream, which diaper(s) includes the taped splice. Consequently, a significant number of diapers are conventionally discarded after each splice to avoid the commercially unacceptable packaging of diapers containing a taped splice.
Splicing machines, which utilize heat-seal splicing techniques instead of tape splicing techniques, have also been employed to splice two-sided plastic material webs. While such machines have the obvious advantage of eliminating the tape, these heat-seal splicing machines require a controlled temperature element adjacent to the webs to be spliced in order to form a heat-seal bond between the webs. The element must be carefully maintained at a predetermined temperature. This typically requires temperature feedback systems to monitor and control the splicing temperature of the heated element. Such control systems are relatively expensive and complicated and require frequent maintenance. Even so, the resulting heat-seal splices often include xe2x80x9ctailsxe2x80x9d or small pieces of the webs adjacent to the location of the splice. Disposable diapers, for example, that include splices having such xe2x80x9ctailsxe2x80x9d are commercially unacceptable, and thus again, a number of disposable diapers may have to be discarded each time a splice is made.
U.S. Pat. No. 4,923,546 is directed to a relatively high speed, web-processing operation, such as a disposable diaper manufacturing line. The patent describes a method and apparatus comprising a splice wheel arm assembly for forming a butt splice to join together a web from a new roll of material to a web that is from an expiring roll of material. To form the butt splice, the leading end of the new web is trimmed by moving one knife wheel assembly along the cutting edge of an anvil. The use of adhesive tape presents problems downstream since the tape must not be in the final consumer product.
U.S. Pat. No. 4,859,270 discloses a web splicing apparatus and method to lap splice together the leading end of a web from a new roll and the trailing end of a web from an expiring roll running under tension and at a relatively high speed, where the new and expiring webs each have identical, spaced, regularly repeating patterns. Securing means, typically pieces of adhesive tape, are used to accomplish the splice.
U.S. Pat. No. 5,514,237 is directed to a method and apparatus for continuously heat splicing thermoplastic webbing. First and second webs of a thermoplastic material are held stationary and heat spliced together by bringing together first and second opposable splicer clamps to form an overlapping area between the first and second webs and by applying a heat impulse to the overlapping area so as to bond the webs together. The overlapping webs are heat bonded in one step, and this requires an expensive heat-splice device.
U.S. Pat. No. 5,669,998, which is assigned to the assignee of the present application, describes a web splicing assembly and method for heat splicing together two webs, addresses the problem of the downstream discarding of disposable diapers every time a splice is made, and is hereby incorporated by reference in its entirety. The disclosed web splicing assembly includes first and second splicing sub-assemblies that are used for heat-seal splicing the trailing end of a first, two-sided plastic material web and the leading end of a second, two-sided plastic material web together; and then after the second web has run, for heat-seal splicing the trailing end of the second web and the leading end of a third, two-sided plastic material web together. The first and second sub-assemblies each have a relatively movable slide bar and a relatively fixed nip bar. The sub-assemblies are each movable between first and second positions. Each slide bar carries a heated wire that heat severs the clamped webs and heat-seals the clamped webs together.
While the apparatus and method disclosed in U.S. Pat. No. 5,669,998 represents a significant step in the development of the art of splicing together web material, there are still problems that need to be addressed. The use of long slide bars for heat-seal splicing together two wider webs can lead to undesirable slide bar flexing and bending problems that can lead to a non-uniform heat-seal splice. To minimize the bar flexing problem, a plurality of pneumatic cylinders are coupled to the slide bar assembly to keep the bar straight. These pneumatic cylinders add to the maintenance and running cost of the web splicing assemblies. Thus, there has been a longstanding need for a simpler apparatus and method for heat-seal splicing two webs together.
Accordingly, a principal object of this invention is to provide an improved, simpler apparatus and method for heat-seal splicing together two webs.
Another object is to provide a heat-seal splice apparatus and method that minimizes the requirement for bulky and expensive pneumatic cylinders and that avoids the non-uniform heat-seal splice problem.
The present invention provides a method for heat-splicing together a trailing end of a first two-sided plastic material web and a leading end of a second two-sided plastic material web. More particularly, the preferred embodiment of the method comprises the steps of: providing a first plastic material web, which web is wound in a rotatable roll; providing a leading end of a second plastic material web, which web is wound in a rotatable roll; clamping together the first plastic material web and the leading end of a second plastic material web; and bringing a heated sealing wire into momentary contact with sequential, transverse portions of the clamped web ends, starting with a portion adjacent to one side edge of the clamped web ends and continuing transversely across the clamped web ends, to heat seal weld clamped web ends together and to sever the trailing end of first web from the first web roll. The method of the present invention is especially suited for heat splicing two-sided plastic material webs and for heat splicing relatively wide webs.
The present invention further provides an apparatus for heat-splicing a trailing end of a first plastic material web, which is wound in a rotatable roll, and a leading end of a second plastic material web, which is wound in another rotatable roll. More specifically, the preferred embodiment of the improved apparatus of the present invention comprises: a traverse cylinder that is attached to a pulley system; a shuttle attached to the pulley system; a movable element attached to the shuttle; a heated sealing wire of sufficient length to traverse the width of the ends of the first and second of the webs to be spliced, the heated sealing wire being disposed in proximity to the movable element; and a spring to bias the movable element into contact with the heated sealing wire and thereby into contact with sequential portions of the web ends, starting with a portion adjacent one side edges of the web ends and continuing transversely across the web end to the other side of the web ends.
The above mentioned and other features of this invention and the manner of obtaining them will become more apparent, and the invention itself will be best understood, by reference to the following drawings taken in conjunction with the accompanying description of preferred embodiments.